With the latest app updates, it now adds EXIF tags to all images before starting the upload. Ity also goes through all images even if they all had EXIF tags already added.
This is especially obvious when working with a larger number of images like 50 000 - add EXIF tags to all of them, have the app crash soon after that and try to upload the images. It goes through all 50 000 images again.

Perhaps the app can mark sequences as done regarding EXIF tags and not waste time on them, or some other mechanism to save the time.